PhD Position : Design and fabrication of an inflatable architectured shell at the civil engineering scale

PhD Position : Design and fabrication of an inflatable architectured shell at the civil engineering scale

Architectured inflatable materials for designing functional Shells

While inflatables of complex 3D shapes can be obtained by assembling carefully designed panels, their fabrication generally requires significant manual intervention as the pieces of the inflatables need to be non-trivially aligned before they are sewn or sealed to each other. When deflated, such structures are notoriously difficult to fold. In contrast, inflatables made of tubular chambers are simpler to fabricate and easy to roll or fold for storage or transportation as they are planar when deflated. However, the high anisotropy of the tubular pattern limits the space of shapes that can be reproduced as well as the strength of the final shell structure. Recent work by members of the consortium showed that it is still possible to program 3D inflatables by playing with the alignment of the tubes (see inset figure). However, these techniques are in practice still limited to a narrow range of axisymmetric shapes despite advances in the geometrical description of the problem. More importantly, the resulting inflatables suffer from poor bending stiffness and limited strength. This stiffness issue limits the use of these inflatable structures for practical applications, as structural rigidity is generally required for the object to be functional.

MatAIRials project tackles these limitations and aims at developing novel tools to easily design and fabricate free-form inflatable shells able to carry external loadings.

The main objectives of the project can be defined as follows:

  • Ease of fabrication: The 3D structures will be made of superimposed planar membranes sealed according to a given welding pattern, a process that can be easily upscaled and automated.
  • Ease of design: The optimal welding pattern should be obtained automatically, i.e., through numerical computation, and propose a numerical tool that can be incorporated into a complete and fully automated design pipeline, from user-specifications to confection details which will be made available to the architecture and designer community.
  • Functionality: A demonstration will be made that the proposed methods can be used for fabricating functional objects (here, able to carry loads). This will be achieved via the fabrication of two types of demonstrators: typically, a functional medical orthosis (small-scale application) and an inflatable formwork (civil engineering application) which is the goal of the present PhD proposal.

To reach these objectives, locally periodic welding patterns, inspired by Origami, will be investigated and the resulting inflated pad will be treated as a meta-material (i.e., an architectured material) whose geometric (metric and curvature changes) and mechanical properties (membrane and bending stiffnesses and strength) will be characterized. Tiling these patterns on the inflatables and adjusting their parameters should then allow to play with the local in-plane contraction of the pad and in turn to control its final 3D shape. Indeed, following a fundamental result from differential geometry, surfaces undergoing non-uniform metric changes become 3D.


An inflated auxetic pad built at Navier


Inflated auxetic pad finite elements simulation by Inria

More info here